Cataract is a disease in which a crystalline lens in the eye functioning as a lens becomes opaque. The opacity prevents sufficient light from entering the eye, resulting in visual impairment. The crystalline lens in the human eye is a transparent convex lens of diameter about 9 mm and thickness about 4 to 5 mm and is positioned behind the iris. The crystalline lens is configured such that a tissue corresponding to the content of the lens and being called a cortex is wrapped with the anterior lens capsule and the posterior lens capsule, each of which is about 10 μm in thickness. The cortex is a soft tissue, but a hard opaque tissue called a nucleus is formed in a central portion of the crystalline lens mainly due to aging. This is the leading cause of cataract. The cataract surgery extracts such an opaque crystalline lens to enable sufficient light to enter the eye, thus recovering vision.
Various techniques for such cataract surgery have been developed such as intercapsular cataract extraction (ICCE) and extracapsular cataract extraction (ECCE). Among these techniques, phacoemulsification is now mainly used because this technique involves a reduced incision size, easy postoperative recovery, and a low incidence of astigmatism. The phacoemulsification includes inserting a surgical instrument through an incision of about 1 to 3 mm formed in the cornea or sclera and manipulating the surgical instrument. This surgery includes using a cystotome needle or forceps to tear the anterior lens capsule that is transparent, has a thickness of about 10 μm, and wraps the crystalline lens to make a continuous circular incision with no gap in a radial direction (this is called continuous circular capsulorrhexis (CCC)) and sucking and removing the content of the opaque crystalline lens through the incision. At this time, the lens nucleus, which is a hard portion formed in the center of the crystalline lens, is grooved and split into small fragments based on various techniques. The respective nuclear fragments are fractured with an ultrasound emulsion instrument and the fractured fragments are aspirated and removed (this is called phacoemulsification). Finally, the opaque cortex between the anterior lens capsule and posterior lens capsule is aspirated and removed so as to leave only a transparent capsular bag formed of the anterior capsule and posterior capsule of the lens. Then, an intra ocular lens (IOL) serving as an artificial lens is inserted through the above-described incision and CCC. Such surgery is performed on at least one million people per year in Japan and on at least three million people per year in the United States.
The ultrasound cataract surgery (phacoemulsification) is a delicate surgery requiring delicate techniques, and surgeons need to deal with a relatively large number of cases in order to improve the skill. However, at present, due to frequent medical lawsuits and a strict requirement to obtain informed consent from patients, training young unskilled surgeons in surgery through clinical practice is difficult. Thus, wet lab surgical training using fresh extracted porcine eyes is most frequently used as training for the cataract surgery. However, the porcine eyes are disadvantageous for the following reasons: the porcine eyes become spoiled easily and thus need to be used early after extraction, the use of the porcine eyes in an operating room is unsanitary, preparing and cleaning up the porcine eyes is cumbersome, and relevant surgical consumables are expensive. In particular, the biggest problem of the porcine eye training is that the anterior lens capsule in the porcine eye is excessively soft and unsuitable for CCC training and that the crystalline lens in the porcine eye includes no nucleus and is formed only of a soft cortex, precluding a lens nucleus splitting technique from being practiced. Thus, there have been several proposals for allowing simulation training of the cataract surgery to be carried out so as to cause a feeling close to that which is generated in the case of the human eyes.
Eye devices developed for cataract surgery practice and using an artificial lens include “Marty the Surgical Simulator” (hereinafter referred to as “Marty artificial eye”, “Phaco Practice Eyes”, “Phak-I™ Surgical Practice Eye” (hereinafter referred to as “Phak I”), and “KITARO DryLab”. Among these eye devices, the “Marty artificial eye” and the “KITARO DryLab” include a replaceable artificial lens portion so that after every surgery practice, only the artificial lens portion is replaced. On the other hand, in the “Phaco Practice Eyes” and the “Phak-I”, an artificial eye device includes a non-replaceable artificial lens portion in an artificial eyeball portion so that after every surgery practice, the whole artificial eyeball portion is replaced.
The “Marty artificial eye” includes an eyeball (orb) that has a chamber formed inside and an opening through which the chamber communicates with the exterior (see Patent Literatures 1 to 4). The opening includes a shelf that accommodates an artificial posterior lens capsule that protrudes toward the chamber, an artificial lens wrapped, at the front and rear thereof, with a thick film serving as an artificial anterior capsule, and a cornea cap in order. In the “Marty artificial eye”, the artificial lens capsule wrapping the artificial lens is formed of a thick film made of vinyl or vinylidene chloride. The excessively hard and thick material of the film substantially precludes the execution of above-described continuous circular capsulorhexis (CCC), which is an essential step for the currently mainstream ultrasonic cataract surgery. Moreover, a hard artificial nucleus is located immediately below the film, and no soft material acting as the cortex exists between the film and nucleus. Thus, disadvantageously, the device has no space to bury an instrument for the CCC such as a cystotome needle or an anterior lens capsule forceps into the lens cortex. The instrument may come into direct contact with the hard nucleus and may be caught thereon. Another reason for the failure to carry out the CCC is that the artificial anterior capsule of the film is fixed so as to be wrinkled and is not tightened at an appropriate tension. The artificial nucleus that is split into fragments which are then ultrasonically fractured is formed of a substance prepared by using gelatin as a main component and adding alginic acid, guar gum, glycol, and gelactasol to the galatin. Thus, the artificial nucleus is difficult to split smoothly and is likely to be collapsed during manipulation. Hence, this surgery is very different from the actual human eye cataract surgery. Additionally, the “Marty artificial eye” itself is a very expensive product, and an artificial cornea and an artificial lens, which are disposable components, are also expensive. Consequently, the “Marty artificial eye” was used only in some facilities, and the manufacturing and supply of this product have been suspended. The greatest cause for the unpopularity of the “Marty artificial eye”, intended for the cataract surgery practice, is that this product fails to allow the surgery to be simulated so as to cause a feeling similar to that which is generated in the case of the human eyes.
In the “Phaco Practice Eyes” (Madhu Instruments, New Delhi, India), an artificial anterior capsule wrapping an artificial lens is formed of a synthetic resin film which appears to be vinyl and is relatively thicker and harder than the human eye lens capsule. With the “Phaco Practice Eyes”, the CCC can be practiced, but a slight variation in force causes an incision to shift in an unintended direction. Thus, this CCC is very different from the CCC carried out on the human eyes. There is another reason that the “Phaco Practice Eye” fails to allow the CCC to be carried out in exactly the same manner as that for the human eyes. That is, a hard artificial nucleus is located immediately below an artificial anterior capsule, and there is no soft that corresponds to the cortex between the artificial anterior capsule and the nucleus. Thus, the device has no space to bury a cystotome needle or a forceps for the CCC into the cortex. The instrument may come into direct contact with the nucleus and may be caught thereon. Additionally, an artificial nucleus that is split into fragments which are then emulsified and aspirated by a surgery device is made of glycerin soap. Thus, the artificial nucleus can be split using an instrument, but when the artificial nucleus is split, there is a strong sense of resistance from the artificial nucleus similar to that which is generated when hard chocolate is broken. The artificial nucleus is broken with a snap, and the resulting split surface is jagged. The artificial nucleus fails to be split with a certain resilience so that the resulting fragments have smooth cross sections as in the case of the human eyes lens. Moreover, it takes long for the ultrasonic surgery device to emulsify and aspirate the fragments of the nucleus, and also in this point, the surgical simulation with the “Phaco Practice Eyes” is different from actual human eye surgery.
In the “Phak I” (EYE CARE AND CURE TUCSON, Ariz., USA) (patent pending), an artificial anterior capsule is formed of a very thick and soft and brittle material and is thus almost impossible to make an incision of the CCC. Furthermore, an artificial nucleus is present immediately below the artificial anterior capsule, and there is no portion forming an artificial cortex below the anterior lens capsule. The artificial nucleus is formed of a very brittle and soft material and is thus difficult to split into fragments. This precludes the ultrasonic cataract surgery from being effectively practiced.
The “KITARO DryLab” (Frontier Vision Co., Ltd., Nishinomiya, Japan) (an application for a patent was filed in Jan., 2009) is an artificial eye device for practicing cataract surgery which has been developed by Akura, who is the inventor of this “Artificial lens for cataract surgery practice.” The device is not intended to allow practice to be carried out using an actual ultrasonic operating deice but is of a type with which practice is carried out on a desk with naked eyes. The “KITARO DryLab” uses an artificial lens formed of an artificial anterior capsule (anterior capsule film), an artificial posterior lens capsule (posterior capsule cup member), an artificial nucleus accommodated in the posterior capsule cup member, and an artificial cortex arranged below the anterior capsule film. The artificial anterior capsule is formed by coating a polyethylene terephthalate (PET) film of thickness 5 μm with a special resin dye. The artificial anterior capsule has a thickness and a tear strength against instruments which are approximate to those of the human anterior lens capsule. An artificial cortex made of soft wheat clay is present below the PET film. When the CCC is carried out, an instrument used is buried in the artificial cortex so that the CCC can be practiced exactly in the same manner as that for the human eyes. However, one artificial nucleus is made of plastics and intended for the practice of manual instrument manipulation. This plastic nucleus cannot be emulsified or aspirated using the ultrasonic surgery device. Another nucleus is made of polymer clay and can thus be split and emulsified and aspirated using the ultrasonic surgery device. However, during the emulsification and aspiration, the polymer clay is always caught in an aspiration line of the surgery device, often suspending the surgery practice for an operation for removing the caught polymer clay. The wheat clay serving as the artificial cortex is also caught in the aspiration line. Thus, it is difficult to practice the surgery based on the ultrasonic cataract surgery device using the artificial lens currently used in the “KITARO DryLab”.
Akura, the inventor, presented a method for practicing the ultrasonic cataract surgery using the “KITARO DryLab” at German Society of Ophthalmology Congress (DOC) in September 2009 (Nuremberg) and at European Society of Cataract & Refractive Surgeons (ESCRS) (Barcelona) in October 2009; the title of the presentation was “KITARO DryLab & WetLab-Handy Surgical Simulate for Practicing Cataract Surgery”. In the presentation, Akura introduced “KITARO WetLab” in which an opening in an upper part of an artificial eyeball portion of the “KITARO DryLab” is closed with a commercially available polypropylene tape so that the resulting “KITARO DryLab is used to practice the surgery based on the ultrasonic cataract surgery device. An artificial nucleus in the “KITARO WetLab” is produced by, when the surgery is practiced, boiling agar together with water on site to prepare an agar solution, and using a syringe to aspirate and inject the agar solution into a plastic cup. An artificial cortex in an artificial lens in the “KITARO WetLab” is made of starch paste. An artificial anterior capsule is made of a PET film of thickness 5 μm, and an artificial posterior lens capsule is made of hard plastics with a given shape. Since the artificial lens used in the “KITARO WetLab” includes the artificial anterior capsule, the artificial cortex, and the artificial nucleus, the “KITARO WetLab” allows simulation training to be achieved which is much more similar to the human eye surgery than the other artificial eye devices for surgery practice. However, the artificial cortex made of starch paste is easily aspirated by the surgery device together with the artificial nucleus when the artificial nucleus is emulsified and aspirated. This precludes the artificial nucleus from being held in a central portion of the artificial lens throughout the emulsification and aspiration operation. Thus, the artificial nucleus migrates freely to prevent effective surgery practice. Furthermore, the “KITARO WetLab” has another disadvantage regarding hydrodissection that is always carried out before a phacoemulsification operation on the nucleus. The hydrodissection is an operation of injecting water into the artificial lens to separate the nucleus portion, the cortex portion, and the lens capsule portion from one another. When the hydrodissection is carried out on the artificial cataract lens with the artificial cortex made of starch paste, the starch paste splashes into a flow of water, and most of the starch paste is lost before the nucleus is emulsified and aspirated. Moreover, the human eye lens cortex has fibrous nature, and the cortex made of starch paste fails to express the nature. This also precludes effective surgery practice.